68 BULLETIN OF THE LABORATORIES 



Although not abundant, this species has been encountered several 

 times. 



Sp. 7- Alona glacialis, Birge. 



Alona glacialis, * C. L. Merrick, Final Report on Minn. 



Crustacea, p. ioo. 

 This species is very scarce. 



Sp. 8. Alona intermedia, Sars. 



Alona intermedia, * C. L. Ilerrick, Final Report on 



Minn. Crustacea, p. ioi; pi. I, fig. 15. 



Sub-genus Pleuroxus. 



Sp. 9. Pleuroxus denticulatus, Birge. 



Pleuroxus denticulatus, * * * C. L. Herrick, Final Report 

 on Minn. Crustacea, p. no; pi. G, figs. 12, 13. 



This species is abundant in all of our canal basins and in several 

 of the larger ponds. 



The number of teeth upon the caudo-ventrad angle of the shell 

 varies from one to three. 



Sp. 10. Pleuroxus hamatus, Birge. 



Pleuroxus hamatus, * * C. L. Herrick, Final Report on 



Minn. Crustacea, p. no; pi. II, fig. I. 



Although not widely distributed, this species is quite abundant in 

 the few canal basins and large ponds where it does occur. 



A few slight deviations from the descriptions that I have seen of 

 this species tempt me to give a complete description. I have not seen 

 Professor Birge's description. Shell long and low, about twice as long 

 as high. Length about 478 micro-millimetres, height about 278 

 micro-millimetres- Caudad margin of shell straight, about two- 

 thirds as high as the greatest height of the shell. Caudo- 

 ventrad angle of shell not toothed, but is margined with min- 

 ute sharp points. Ventrad margin straight or feebly concave, 

 supplied with a fringe of long hairs. Beak curved caudad, about 

 twice as long as the antennules, including hairs. Shell is coarsely 

 marked with the same lines that adorn the shell of P. denticulatus. 

 In addition, the whole shell is closely striated with fine, undulating, 

 sub-parallel, longitudinal, lines. These striations extend out upon the 

 beak. Eye larger that the pigment fleck. First foot of the female 

 supplied with a claw. The post abdomen is long, slender, truncated. 



